Do i need to connect my arduino uno ground while having an external power ?

Hi,

Sorry i certainly a stupid question but i like to make sure i do thing in the right way.

I have some component in a breadboard that use a lot of power ( more than what my arduino can provide ). So i have an external power connected to the breadboard. The Atmega is still on the arduino board and i am using digital pin to communicate with the component on the breadboard. Do i need to connect the GND pin of my arduino to the GND on the breadboard ? ( which is connected to an external power) . I am doing that right now because i thought it was correct ( not sure) but i like to know the why.
Thanks in advance

All the best

Vincent

Always connect the grounds together. Among other things, the ground connection defines zero for the signal levels on Arduino pins.

Thanks a lot

If you are unsure about the GND, think of a simple battery (cell)

If you connect only the positive end to your circuit, what happens? That's right, absolutely nothing.

The key word here is "Electronic Circuit" - it needs to be a closed 'circuit' for current to flow.

With the exception on radio transmission, you always need the ground.

See this:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html